1.plasma
2.frag
3.pulse
Pulse, thank me later.
You should make this thread a poll.
Pulse is a great tactical grenade. I never use frag anymore, only plasma and pulse.
If you’re skilled with a frag you can actually bounce the grenade perfectly around a corner and kill an enemy player. No other grenade has that capability. Therefor I use frags more then plasma’s or pulse
I like frags because of the bounce/angle options.
Pulse.
Frag is, mathematically and in practicality, the best one. It’s not disputable.
However, the most worst and yet the most FUN one to use is the Pulse.
frags are good for bouncing and getting that extra damage on someone to set the advantage in your favor.
pulses are more area of effect but with the right throwing you can strip an attackers shields, better for a more defensive nature.
plasma, best imo, if anyone ever gets the drop on you just throw them in the general direction and you can usually trade kills even if your unaware, also just throw them at vehicles and your guaranteed a free vehicle kill too. When in doubt just press the left trigger over and over over and you win 
Plasma grenade for Slayer gametypes.
Pulse grenade for Objective gametypes. It’s so fun to see players crowding around a hill or oddball, and you just throw a Pulse grenade in there.
Sticky. If it sticks they’re dead!
Frags can bounce and pulse is great either if they are afk or you’re assaulting a fortified position like in king of the hill or dominion.